Screening and feeding device for cellulose digesters

ABSTRACT

A cellulose digesting apparatus having at least one vertical digester in open communication with a pressure-resistant vessel containing a screening device, the screening device comprising a shell having an upper impervious portion and a lower strainer portion, wherein liquid is strained from a chips-liquid suspension for recirculation of the liquid, and a feeding device which is adapted to transfer the chips from said vessel to the digester, around the shell a circular trough for collecting chips discharged over the top edge of the impervious portion, the feeding device comprising a plurality of chips outlets in the vessel each adapted for connection to a separate digester and a distributing device for the distribution of the chips upon the outlets used.

United States Patent 1191 Richter 1 1 1 3,849,247 Nov. 19, 1974SCREENING AND FEEDING DEVICE FOR 3,471,366 10/1967 126111113111 162/237CELLULOSE DIGESTERS 3,586,600 6/1971 Rich et a1. 162/246 X 3,681,1928/1972 Reinhall 162/52 X Inventor: Johan Richter, St. Jean p 3,743,5727/1973 Richter 162/237 x Ferrat, France [73] Assignee: Kamyr Aktiebolag,Karlstad, Primary Examiner-5 Lfion Bashol'e S d Assistant ExaminerStevenM. Alvo Attorney, Agent, or FirmCushman, Darby & [22] Filed. Mar. 12,1973 Cushman [21] Appl. No.: 339,758

[57] ABSTRACT Foreign Application Priority Data A cellulose digestingapparatus having at least one Mar. 21, 1972 Sweden 72/3600 verticaldigester in open communication with a pressure-resistantvesselcontaining a screening device, the [52] US. Cl 162/237, 159/23, 162/52,screening device comprising a shell having an upper 162/241, 162/246,210/415, 214/ 17 C impervious portion and a lower strainer portion, [51]Int. Cl. D2lc 7/06 wherein liquid is strained from a chips-liquidsuspen- [58] Field of Search 162/246, 241, 242, 237, sion forrecirculation of the liquid, and a feeding de- 162/52, 17; 214/17 C;259/23, 8; 210/413, vice which is adapted to transfer the chips fromsaid 414, 415; 100/117 vessel to the digester, around the shell acircular trough for collecting chips discharged over the top [56]References Cited edge of the impervious portion, the feeding deviceUNITED STATES PATENTS comprising a plurality of chips outlets in thevessel each adapted for connection to a separate digester 31323111;11132? 21323131113311: '11: 1231321? and a ttttttttttttttt ttttttt tottttt tttttttttttttt of the 3,041,232 6/1962 Richter 162/52 x c111pS Pthe Outlets used- 3,294,626 12/1966 Mathews 162/246 X t 3,467,573 9/1969Vogel 162/237 x 6 4 f F'gures 57 47 4 m *3 0o 1- g T o d U o 0 0 e "t 49g l a 0 1 o :-?Z 0g %g "8 7 I 13, l 0% I 970 0 .63 03036 33 .53

1 1 25 LAAJ A SCREENING AND FEEDING DEVICE FOR CELLULOSE DIGESTERS Thisapplication is related to U.S. Ser. No 339,761 filed Mar. 12, 1973 byOliver Laakso.

The invention relates to cellulose digesting apparatus for the chargingof chips to a digester which is in open communication with a separatepressure-resistant vessel containing a screening device which strains achips-liquid-suspension in order to recycle the liquid, and a feedingdevice for the transfer of the chips from said vessel to the digester.An example of a digester is shown in the U.S. Pat. No. 3,429,773.

The invention is concerned with the problem that cellulose mills oftenare in continuous expansion, and therefore, after only a few yearsproduction, a new digesting plant may have to be increased in capacity.An object of the invention is to effect in a simple manner and at acomparatively small cost, a desired expansion so that cellulosedigesting plants can be expanded with the greatest possible use of theequipment already installed, i.e. with as little rebuilding thereof aspossible. Thus, the invention is directed at using the installed devicesfor pretreatment of the chips and transportation thereof to the digestertop; if at a later stage it is desired to enlarge the digesting plantwith one or more further digesters, only simple modifications need bemade.

\ phate, sulphite, or soda liquor.

These objects are achieved by providing a pressureresistant vessel witha plurality of chips outlets, each adapted for connection to a separatedigester, allowing the plant to be supplemented with one or moreadditional digesters. Further, a device is provided for the properdistribution of the chips into the outlets employed. According to apreferred embodiment, the upper end of a vertical cylindrical separatingshell surrounds a feeder screw coaxial therewith, and feeds the chipsupwardly. This upper end is surrounded by a portion of the pressurevessel preferably forming a circular trough with downwardly slopingchips outlet tubes being connected to the bottom of said trough at alevel lower than the upper edge of said separating shell, so that chipsflowing over said edge are transferred to the digester or digesterssubstantially by the action of gravity.

BRIEF DESCRIPTION OF THE DRAWINGS Y The preferred form of the inventionwill now be described more particularly with reference to theaccompanying drawings wherein:

FIG. 1 diagrammatically shows a cellulose digesting apparatus comprisingtwo digesters,

FIG. 2 is a vertical elevational and partially crosssectional view shownat an enlarged scale, of the screening and chips distributing vesselforming part of said apparatus;

FIG. 3 is a modified form of the invention shown in FIGS. 1 and 2, FIG.4 is a partial cross-sectional view taken along lines 4-4 of FIG. 2,with chips removed, showing exemplary displaceable lids for varying thesize of the chips outlets.

DETAILED DESCRIPTION The apparatus in FIG. 1 comprises two verticalessentially cylindrical continuous digesters 11, 13, the upper ends ofwhich are continuously fed with a mixture of chips and digesting liquor.From the lower ends of the digesters l1, l3 digested and partiallywashed cellu- The chips are pretreated and distributed to each of thedigesters. Chips from chips bin are fed in the usual manner through alow-pressure valve 17 into a steaming vessel 19 wherein the chips aresteamed with low-pressure steam. By means of a high-pressure transfervalve 21 the chips are then transferred'to a conduit 23 filled with thedigesting liquor at approximately the digester pressure. The conduit 23is connected to a vertical, conical impregnating vessel 25 whosecircumference increases with its vertical longitudinal axis. The vessel25 is united with the pressure-resistant vessel 27 which encloses ascreening device and a chips distributing device. Liquid screened off bysaid screening device in vessel 27 is returned through the conduit 29 tothe high-pressure transfer valve 21. Pump 31 circulates the liquid in aloop over 21, 23, 25,27, and 29. In said loop the chips are introducedby means of the valve 21 so that the chips suspended in the liquid areflushed into the vessel 27 situated at the level of the digester topsand are delivered and retained therein, whereas the liquid of thesuspension is separated and recirculated.

The vessel 27, shown partially in sections in FIG. 2, is provided withina pressure-resistant casing 33 and a vertical cylindrical separatingshell 35 of the same diameter as and forming an extension of the upperend of the impregnating vessel 25. The lower end of the separating shell35 is perforated or shaped with slits'so as to form a strainer, whereasthe uppermost portion of the separating shell is impervious and forms apartition. Inserted into the shell is a feeder screw 37 attached to avertical shaft 39 which extends through and is sealed to the lid 41 ofthe casing 33. A motor 42 (FIG. 1) connected to the exterior end of theshaft 39 turns the feeder screw 37 causing the chips-liquor-suspensionto move-upwardly within the separating shell 35. Excess digesting liquoris drained through the straining apertures of the shell into the spacebetween the shell 35 and the casing 33 and then into the conduit 29 backto the high-pressure transfer valve 21, whereasthe chips are raised overthe edge 43 of the shell 35. Usually a free liquid surface is maintainedat a level 45 within the impervious upper portion of the separatingshell. When the chips have been raised above said level, entraineddigesting liquor drains off, so that the chips traveling over the edge43 merely contain digesting liquor absorbed in the pores of the fibermaterial or superficially adhered thereto.

Vessel 27 forms a steam-filled space, surrounding the upper edge 43 ofthe separating shell, the lower boundary of which forms a circularlaunder or trough 47. Said trough 47 extends around the upper edge 43 ofthe separating shell 35 and has its bottom situated at a lower levelthan said edge, so that chips fed upwardly through the shell by means ofthe feeder screw 37, drop over the edge 43 down into the trough 47 bygravity. Connected to the bottom of the trough are at least twodownwardly sloping chips outlet tubes 49, 51, which by means ofconnecting tubes 53 and 55 may be connected to the separating digestersl1 and 13. Said tubes form an open communication between the vessel 27and the respective operating digester, but it may be advantageous toinsert shut-off valves in the conduits 53, 55 in order to be able tooperate one digester without interruption when the other is temporarilytaken out of operation.

According to the invention, the vessel 27 is provided with a device fordistributing the chips upon the chips outlets 49, 51. In the embodimentshown in FIG. 2 said distributing device consists of a scraper attachedto the shaft 39 which comprises scraper arms 57 projecting radiallyacross the edge of the shell 35 and down into the bottom of the trough47. Chips that drop over the edge 43 down into the trough 47 arecollected by said rotary scraper arms and are carrying along until theydrop into the chips outlet tubes 49, 51. With diametrically oppositelocations of two outlets the chips will be distributed into equal partsinto each outlet. When the digesters are of different sizes orcapacities so that distribution of the chips may be required indifferent proportions, the location of the outlets on the periphery maybe changed accordingly. If, for example, one digester requires twice asmany chips as the other, the outlets are placed at an angle of 120degrees from each other, whereby the scrapers collect and transfer tothe smaller digester the chips which have dropped into one third of thecircumference of the trough, and collect and transfer to the largerdigester chips which have dropped into the remaining two thirds of thecircumference of the trough. Obviously, the desired distribution mayalso be attained by varying the size of the outlets. Variations of bothsize and angle can be brought about by displaeeable lids, such as lids50 shown in FIG. 4, in the bottom of the trough 47.

The drawings refer to an apparatus comprising two digesters, but theapparatus may be operated with a single digester, as is shown in FIG. 2by the digester 13 with dash lines. In this latter case the chips outlet51 is blocked, eg by means of a blind flange at its lower end, and thescraper arms 57 are not used for their distributing function but merelyfor moving the chips in the trough to the single outlet 49.

Of course, the number of chips outlets may be increased and it ispossible to use a distributing vessel with three, four or more chipsoutlets that are used according to the total required output of thedigesting apparatus.

The entire quantity of digesting liquor required for the digestion issupplied through the conduit 61 and high-pressure pump 63 after havingbeen mixed with the liquor transferred to the low-pressure side of thetransfer valve 2i, which is returned via the screening device 65 and thetank 67. A portion of the liquor supplied is transferred into theconduit 29 by the valve 69 which is controlled by the level 45 in thevessel 27 so as to maintain said level, whereas the remaining portion ofthe liquor supplied is pumped through the conduit '71 directly to thedigester tops and distributed by means of the valves 73, and 75.Preferably, said liquor portion is introduced into the conduits 77 and79 along with pressure steam to the digesters for heating the chipstherein to digesting temperature. In this manner the liquor will beatomized and sprayed as a mist over the chips in the digester tops.

As an alternative, all digesting liquor may be supplied to the vessel27. This is preferred when the chips are able to absorb a sufficientquantity of liquor, so that a free liquor level 45 will be maintainedbelow the edge of the straining portion of shell 35 without requiringany particular level control. On the other hand, if the liquor is toflow over that edge 43, procedures should be taken to distribute theliquor properly into the digesters.

The above-described embodiment merely constitutes an example of theapplication of the invention and may be modified as to its detailswithin the scope of the following claims. Thus the apparatus can also beoperated when the digesting liquor or the main part thereof is supplieddirectly to the digesters and such liquid as is required for suspendingthe chips and flushing them to the digester tops consists of water, asis the case in prehydrolysis digesters, or of more or less diluted whiteliquor or black liquor.

In another embodiment of the invention shown in FIG. 3, the inlet to thebottom of the vessel 27 has been modified by the addition of a chamber26 and secondary scraper 28. The section 26 effectively increases thetotal volume of pipe 25 thereby providing for a longer retention time ofthe chips in the feeding line; that is, chips are impregnated in liquidat full digester pressure.

The chamber 26 may be a conical pipe connection and 28 is a rotatingscraper body which will facilitate the chip movement from the largerpipe to the smaller diameter entrance 38. The scraper rotates togetherwith screw 37. The lower end of the screw shaft of FIG.

2 may have a downwardly pointing conical nose to decrease the resistanceagainst the chip flow. However, by providing a larger feeding pipe as in25-26 of FIG. 3, the cone can be omitted and the scraper 28 substitutedby coupling the screw 37 to the scraper shaft. The scraper itself can besupported by the bearings in the bearing housing which in turn issupported by arms fastened to pipe connection 26.

What is claimed is:

l. A cellulose digesting apparatus in which a top portion of at leastone vertical digester is in open communication with a pressure-resistantvessel containing a screening device wherein liquid is strained from achips-liquid suspension for recirculation of the liquid, and a feedingdevice for transferring the chips from said vessel to the digester, saidfeeding device comprising a plurality of chips outlets in the vesseleach for connection to a separate digester and a distributing device forthe distribution of the chips upon the outlets used, said screeningdevice comprising a separating shell having an upper impervious portionand a lower strainer portion including means for collecting liquidseparated from the chips; means for feeding the strainer chips upwardlythrough the shell for discharge over the top edge of the upperimpervious portion, said means including a feeder screw surrounded bysaid shell and coaxial therewith; collecting means around said shell andbelow the top edge of said impervious portion for collecting strainedchips discharged therefrom, said collecting means comprising a circulartrough; the chips outlets comprising tubes connected to and slopingdownwardly from the bottom of said trough for discharge into saiddigestors substantially by gravmy.

2. Apparatus according to claim 1 wherein the distributing devicecomprises one or more scraper arms extending radially beyond theseparating shell into the circular trough and being attached to anddriven with the feeder screw.

-3. Apparatus according to claim 2 wherein the out-' 6 I lower openingtherein and the impregnation vessel includes a frusto-conical sectioncoupled to the pressureresistant vessel at its lower opening; the top ofthe impregnation vessel has a second scraper'in the frustoconicalsection which includes radially extending arms coupled at a center huband driven by the feeder screw.

6. Apparatus according to claim 1 further comprising means for varyingthe size of the chips outlets to effect a desired distribution of chipsto chips outlets.

1. A cellulose digesting apparatus in which a top portion of at leastone vertical digester is in open communication with a pressure-resistantvessel containing a screening device wherein liquid is strained from achips-liquid suspension for recirculation of the liquid, and a feedingdevice for transferring the chips from said vessel to the digester, saidfeeding device comprising a plurality of chips outlets in the vesseleach for connection to a separate digester and a distributing device forthe distribution of the chips upon the outlets used, said screeningdevice comprising a separating shell having an upper impervious portionand a lower strainer portion including means for collecting liquidseparated from the chips; means for feeding the strainer chips upwardlythrough the shell for discharge over the top edge of the upperimpervious portion, said means including a feeder screw surrounded bysaid shell and coaxial therewith; collecting means around said shell andbelow the top edge of said impervious portion for collecting strainedchips discharged therefrom, said collecting means comprising a circulartrough; the chips outlets comprising tubes connected to and slopingdownwardly from the bottom of said trough for discharge into saiddigestors substantially by gravity.
 2. Apparatus according to claim 1wherein the distributing device comprises one or more scraper armsextending radially beyond the separating shell into the circular troughand being attached to and driven with the feeder screw.
 3. Apparatusaccording to claim 2 wherein the outlets are varied with respect toposition about the trough so as to vary proportions of chips input intosaid outlets.
 4. Apparatus according to claim 1, which further includesan impregnation vessel coupled to the pressure-resistant vessel which isadapted to impregnate the chips therein with digesting liquor atessentially the pressure of the digester.
 5. Apparatus according toclaim 4 wherein said distributing device comprises a first scraper andwherein the lower portion of the pressure-resistant vessel has a loweropening therein and the impregnation vessel includes a frusto-conicalsection coupled to the pressure-resistant vessel at its lower opening;the tOp of the impregnation vessel has a second scraper in thefrusto-conical section which includes radially extending arms coupled ata center hub and driven by the feeder screw.
 6. Apparatus according toclaim 1 further comprising means for varying the size of the chipsoutlets to effect a desired distribution of chips to chips outlets.